The present invention pertains to an optical member that is formed using a mold and which is primarily made of a resin, and more particularly, to an optical member that is used in a laser scanning optical system employed as a writing optical system in a laser printer or digital copying machine, for example.
The optical member used in a scanning optical system in a number of instances is a resin molded lens because of the complexity of the functional surfaces, i.e., toric free-form surfaces. In the area of such resin optical members, a technology in which a protrusion indicating the molding information is formed on the plastic lens itself has been proposed as disclosed in Japanese Laid-Open Patent Application Hei 6-75181, for example.
However, the protrusion located on a conventional plastic lens is a code signal to read lot information used for lot control in accordance with which molding machine formed the lens and the location at which the protrusion is formed has no meaning in itself, and the protrusion is located on a surface that is not contiguous to the functional surface of the lens. Consequently, a problem arises as described below.
Using the information obtained from the protrusion on the lens, configuration or reference line discrepancies in the lens surface molded by the molding machine cannot be detected. Moreover, it is difficult to detect these discrepancies from the lens itself where the lens lacks any positional references having a specific relationship to the lens surface.
In other words, the protrusion provides locational information useful for the purpose of lot control only, and does not contribute to the measurement of variations among lenses in the same lot formed using the same molding machine. Making adjustments based on the protrusion may correct discrepancies between lots (molding machines), but cannot eliminate variations within the same lot. The protrusion does not contribute to the improvement of precision of the lens surface or of the position of the lens surface relative to reference positions.
Even if locational information to detect the discrepancies were formed on a surface that is not contiguous to the lens surface, as in the case of the protrusion in the conventional art (on the rib, top surface, bottom surface or side surface, for example), because the surface on which the protrusion would be located differs from the lens""s functional surface in terms of the coefficient of contraction, the locational information would be easily affected by discrepancies created during formation. If necessary information regarding the configuration or positions were to be detected based on such information, errors would be included in the detection results.
As a result of this situation, in a lens configuration where the toric functional surface is asymmetrical with regard to a line, as in the case where the toric functional surface is a free-form surface, or in a mold that is used to form such a lens surface, the following is further desired.
In the processing of the cores, which are the molds to form the lens""s functional surfaces, since some molds are designed to be asymmetrical, or where the mold is designed to be symmetrical, since there is a possibility that the formed lens""s functional surface will be unable to fit the mold surface due to processing limitations, or that the functional surface will become asymmetrical due to the deformation during contraction, it is necessary to make clear at the time when the lens is evaluated the lateral orientation of the cores during processing.
In addition, during the measurement of the lens, it is important to accurately measure the configuration of the lens itself, without referring to the positional reference located on the outer circumferences not contiguous to the lens""s functional surface, and is moreover necessary to accurately detect the distance between the reference position on the outer circumference and the central axis that should coincide with the lens""s optical axis.
Further, it is necessary to confirm that the light path is located as designed when seen along the length and width of the lens surface and to make necessary adjustments when the optical member is assembled into the housing.
It is also necessary to remove any positional discrepancies when assembling the cores that comprise the molds to form the functional surfaces on the entry and exit sides of the lens.
The object of the present invention is to provide an optical member satisfying the requirements described above that permits accurate measurement of the lens surface as well as accurate assembly adjustment and confirmation.
In order to achieve the object described above, the optical member of the present invention is an optical member having a toric functional surface comprising a marking which is made by a configuration of a mold used to form the optical member and is formed outside an effective area of the functional surface of the optical member.
Using the construction described above, because the marking is formed outside the effective area of at least one functional surface of the optical member having a toric functional surface, i.e., on part of one functional surface subject to one coefficient of contraction, and are simultaneously formed using the same mold as the functional surface, the markings""positional relationship with the functional surface is determined almost unconditionally without being affected by the difference in coefficient of contraction among various parts of the optical member during formation or by discrepancies between the molds in terms of assembly position. Consequently, there are few discrepancies between the molding surface and the molded surface.
Another aspect of the present invention is an optical member having a toric functional surface for a scanning optical system comprises a marking which is made by a configuration of a mold used to form the optical member which is formed outside an effective area of scanning lens surfaces of the optical member.
Using the construction described above, a marking is formed outside the effective area of the scanning lens surface. Using the markings formed corresponding to the configuration of the molding surface as measurement references, the complex three-dimensional configuration of the toric functional surface of the optical member used for a scanning optical system, as well as the position at which the optical member should be placed, may be easily determined and appropriate adjustments may be made, as in the case of the construction described above.